The present invention relates to an articulating head for a work-probe holder of a coordinate-measuring instrument, having at least two motor-driven axes of probe-holder orientation, and to a method for the coordinate measurement of workpieces by means of such an articulating head.
Articulating devices of the character indicated serve primarily to angularly orient the probe holder used for coordinate measurement of workpieces in such manner that the probe holder can be optimally employed for the desired measurement task.
Since the positions in which the probe head is oriented in the course of a measurement program must be reproducible with a high degree of precision, the articulating mechanism in articulating heads relies upon detent retention of predetermined angular orientations. The location of work-contact probe balls of the probe head are calibrated once in each of the plural detent-retainable positions of the articulating head. The probe holder can thereupon, during the course of a given measurement program, be brought into each of a plurality of different angular positions, which as a rule differ from each other by about 7.5.degree., without need to recalibrate a probe ball.
Articulating probe-holder devices of the indicated type are illustratively known from Federal Republic of Germany Pat. No. 2,804,398, and from corresponding U.S. Pat. Nos. 4,313,263 and 4,571,847, as well as from the following company publications:
1. "3-Dimensional Probes for Coordinate-Measuring Machines", Renishaw Plc., Great Britain, Print Identification BMM No. 1984, 8M 586.
2. Product Information "Handachse" of the Stiefelmayer Company, Esslingen, Print Identification No. 27 04 87-000970.
The advantage of the known articulating devices is that precision bearings are not necessary since the detents determine the position of the probe pin. Furthermore, no position-measurement system is required for each of a plurality of articulated orientations. On the other hand, it is disadvantageous that when using these known devices, one is restricted to given angular orientations of the probe holder. It is therefore not possible to perform active scanning motion or to have probe-holder orientation track surface geometry of a workpiece, in the course of a scanning program. Furthermore, a calibration process is necessary for each detent-retained angular position and for each scanner.
From Federal Republic of Germany Pat. No. 3,322,714, it is known to employ two-axis articulation for orienting an optical probe head over the surface geometry of a workpiece, in the course of scanning movement along a workpiece. To measure the involved angles of displacement, angle-stepping transmitters are provided in the two articulation axes. However, from this German patent, it does not appear how the coordinates of the workpiece-measurement points are determined from the linear-measurement scales of the involved coordinate-measuring instrument and from the angle-stepping transmitters of the involved two-axis articulation.